1. Field of the Invention
The invention relates to multiphase reactors and to a device and method for distributing fluid into a monolith bed.
2. Background Art
Monoliths contain a large number of thin, parallel, straight channels through which fluids, i.e., gas and liquid, can flow. Typically, the channel shape of the monolith is cylindrical. The number of channels in relation to the cross-sectional area of the monolith is referred to as cell density. The cross-section of the channels can be of any arbitrary shape, such as square, rectangular, triangular, hexagonal, circular, etc. Longitudinal fins may also be incorporated in the walls of the channels to increase the surface area of the channels. Monoliths are typically extruded from a ceramic material such as cordierite but may also be manufactured from metal. The walls of the monolith channels may be coated with a porous washcoat containing an active catalyst. Alternatively, an active catalyst may be incorporated into the walls of the monolith channels. In operation, fluids containing reactants flow through the monolith channels. The reactants react in the presence of the active catalyst, and the products of the reaction are transported out of the monolith channels.
Monolithic catalysts are well-known for their use as three-way catalytic converters in automobiles. Their low pressure drop for gas-phase reactions allow them to be placed directly into the exhaust pipe of an automobile without affecting the performance of the engine. Monolithic catalysts are also widely used for cleaning of industrial flue gas. In recent years, monolithic catalysts have been proposed as alternatives to randomly packed pellets in multiphase reactions, e.g., gas-liquid catalytic reactions such as hydrogenation and hydrotreating. One advantage of monolith catalyst beds over random packed beds with conventional catalyst pellets is increased contact efficiency between the reactants and the catalytic layer. Monolith catalysts can be used in both co-current and countercurrent reactor flow configurations, where the reactor flow configuration is determined by the specific reaction processes.
In any multiphase reaction involving a solid catalyst bed, uniform distribution of fluids into the bed is crucial to achieving high process efficiency. Current commercial-scale liquid distributors for trickle flow reactors and other multiphase applications involving random packed beds of catalyst have very low drip point densities, typically less than 330 drip points per square meter, and yet these drip point densities are considered adequate for these applications due to the inherent interconnected interstitial spaces in a random packed bed. Such distributors with each drip point typically covering a minimum area of 4.5 in2 would be inadequate for monolith catalyst beds in practical applications. This is because monolithic catalysts have many small nearly-independent flow channels per cross-sectional area, typically 50 to 600 channels per square inch of cross-sectional area (cpsi). As an example, a 100 cpsi monolith packing has 450 channels in a 4.5 in2 area. A single drip point covering a minimum area of 4.5 in2 would not be able to uniformly distribute fluid into the 450 individual channels in the 4.5 in2 area.